/*
 * Copyright 2002-2020 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.http.codec.json;

import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;
import java.util.Map;

import com.fasterxml.jackson.databind.ObjectMapper;
import org.reactivestreams.Publisher;
import reactor.core.publisher.Flux;

import org.springframework.core.ResolvableType;
import org.springframework.core.codec.StringDecoder;
import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.core.io.buffer.DefaultDataBufferFactory;
import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;
import org.springframework.lang.Nullable;
import org.springframework.util.MimeType;
import org.springframework.util.MimeTypeUtils;

/**
 * Decode a byte stream into JSON and convert to Object's with Jackson 2.9,
 * leveraging non-blocking parsing.
 *
 * @author Sebastien Deleuze
 * @author Rossen Stoyanchev
 * @see Jackson2JsonEncoder
 * @since 5.0
 */
public class Jackson2JsonDecoder extends AbstractJackson2Decoder {

    private static final StringDecoder STRING_DECODER = StringDecoder.textPlainOnly(Arrays.asList(",", "\n"), false);

    private static final ResolvableType STRING_TYPE = ResolvableType.forClass(String.class);


    public Jackson2JsonDecoder() {
        super(Jackson2ObjectMapperBuilder.json().build());
    }

    public Jackson2JsonDecoder(ObjectMapper mapper, MimeType... mimeTypes) {
        super(mapper, mimeTypes);
    }

    @Override
    protected Flux<DataBuffer> processInput(Publisher<DataBuffer> input, ResolvableType elementType,
                                            @Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {

        Flux<DataBuffer> flux = Flux.from(input);
        if (mimeType == null) {
            return flux;
        }

        // Jackson asynchronous parser only supports UTF-8
        Charset charset = mimeType.getCharset();
        if (charset == null || StandardCharsets.UTF_8.equals(charset) || StandardCharsets.US_ASCII.equals(charset)) {
            return flux;
        }

        // Potentially, the memory consumption of this conversion could be improved by using CharBuffers instead
        // of allocating Strings, but that would require refactoring the buffer tokenization code from StringDecoder

        MimeType textMimeType = new MimeType(MimeTypeUtils.TEXT_PLAIN, charset);
        Flux<String> decoded = STRING_DECODER.decode(input, STRING_TYPE, textMimeType, null);
        return decoded.map(s -> DefaultDataBufferFactory.sharedInstance.wrap(s.getBytes(StandardCharsets.UTF_8)));
    }

}
